The present invention relates generally to continuous web cutters and, more particularly, to the feeding speed of the web cutter.
Continuous web cutters are known in the art. As shown in FIG. 1, a continuous web cutter is used to provide cut sheets to an envelope insertion station in a typical envelope inserting machine. Typically, a continuous web of material with sprocket holes (or tractor pin-feed holes) on both sides of the web is fed from a fan-fold stack, or a roll, into the web cutter, which has two moving belts with sprockets (or tractors with pins) to move the web toward a guillotine cutting module for cutting the web cross-wise into cut sheets. Perforations are provided on each side of the web so that the sprocket hole sections of the web can be removed from the cut sheets prior to moving the cut sheets to other components of the envelope inserting machine. In particular, the continuous web cutter, as shown in FIG. 1, is used to feed two webs of material linked by a center perforation. As shown, a splitter is used to split the linked webs into two separate webs before the webs are cut by the cutting module. In general, the web material is driven in move-and-pause cycles, wherein the web material is temporarily paused for a short period to allow the cutter to cut the material into cut sheets. Thus, in each cycle, the web must be accelerated and decelerated. When the acceleration is high, the forces created by the acceleration of the web mass by the driving belt can break the web at a perforation or cause the sprocket holes to tear. Thus, a jam occurs. When high throughput (20,000+cycles per hour) is desired, the acceleration force-induced rip on the sprocket holes is a major limiting factor to the obtainable cycle rate. Furthermore, when the acceleration is high, another force is created by aerodynamic effects, due mainly to wind resistance against the motion of the web. The aerodynamics related force may also break the web at a perforation. For this reason, web cutters are usually operated at a cycle rate much lower than the obtainable cycle rate, affecting the throughput of the envelope inserting machine.
It is advantageous and desirable to provide a method to improve the throughput of web cutters.
It is a primary object of the present invention to improve the throughput of a continuous web cutter by increasing the cycle rate, while avoiding or reducing the web breakage due to the forces resulting from high acceleration of the web mass. The web mass is fed into the web cutter in move-and-pause cycles to allow a cutter to cut the web into cut sheets when the web mass comes to a pause. It is preferable that the speed profile of the web in each cycle includes an acceleration section, a constant speed section and a deceleration section, with the constant speed in the cycle being referred to as a top-out speed. Accordingly, the above-mentioned object can be achieved by the method of the present invention. The method comprises the steps of feeding the web in the first cycle with the top-out speed equal to a first speed, and feeding the web in the following cycles with the top-out speed being progressively greater than the first speed until the top-out speed reaches a second speed.
In that respect, the web cutter is operated in two states. In the startup state, the cycle rate is continually increased from a low rate to an optimized rate. In the steady state, the cycle rate is substantially constant. Preferably, the optimized rate is the highest cycle rate obtainable in the web cutter without inducing breakage in the web. The highest obtainable rate is determined by many factors. These factors include the material strength of the web and the perforation. The factors may also include how the web is supplied from a fan-fold stage or a roll and whether the roll is actively driven by a driving mechanism. Preferably, the starting low rate is equal to about 60% of the highest obtainable rate. However, the Starting low rate is also determined by similar factors. In addition, the starting low rate may also be determined by how the web is accelerated in the acceleration section. For example, the acceleration can be linear or non-linear and the acceleration rate can be high or low.
Furthermore, when the web cutter is still in the startup state, the increase of the cycle rate can be linear or non-linear.
The method, in accordance with the present invention can be implemented in a continuous web cutter by a device of the present invention. The device comprises a speed controller for feeding the web in the first cycle with the top-out speed equal to a first speed, and feeding the web in the following cycles with the top-out speed being progressively greater than the first speed until the top-out speed reaches a second speed; and an input device, operatively connected to the speed controller, for adjusting the first speed, the second speed and the cycles between the first and second speeds according to the web material.
The present invention will become apparent upon reading the description taken in conjunction with FIGS. 2a to 5.